Q:Why
doesn't Vimage offer a 300-MHz card for the machines mentioned in the
title?

A: The cooling requirements of the x4xx/x5xx are such that a silicon-300
MHz CPU (without a fan) will run hotter than the machine can comfortably
tolerate. This especially holds true for the Twentieth Anniversary
Mac, whose internal design makes even a 240-MHz silicon chip inappropriate

By using too hot a CPU, you may upgrade your computer's performance
in the short term; but, as the weeks and months go by, you can expect
to find your machine's health in increasingly sharp decline.

Although somewhat more expensive, a copper CPU will run much cooler,
and not cause long-term damage to your computer that may not be apparent
over the first couple of weeks or months of use.

The market right now is such that copper CPU upgrade cards are somewhat
over a thousand dollars. It is extremely likely that anyone who tries
selling you a "much cheaper card that is made of copper"
is either (better case) misinformed, or (worse case) being "economical"
with the truth.

With technology, perhaps more than most other things, you really
do get what you pay for.